Summary of Key Points
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Scheuermann kyphosis is the most common cause of hyperkyphosis in adolescence.
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There appears to be a major genetic contribution to the etiology.
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The natural history of Scheuermann kyphosis is not well documented.
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Radiographic criteria for Scheuermann kyphosis include wedging of three contiguous vertebrae.
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Treatment of Scheuermann kyphosis is conservative in most situations; however, it is always a multifactorial decision.
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Surgical approach to Scheuermann kyphosis can be anterior only, posterior only, or combined.
Scheuermann Kyphosis
In 1920, Holger Werfel Scheuermann, a Danish surgeon, described a rigid kyphosis of the thoracic or thoracolumbar spine occurring in adolescents. Scheuermann disease was first described as a painful, fixed, dorsal kyphosis of wedged vertebrae, with disturbances of the vertebral end plates. Sorensen later proposed the now widely accepted radiographic criteria of three adjacent wedged vertebrae, angled by at least 5 degrees. It is the third most common cause of back pain in children and adolescents following spondylolysis and spondylolisthesis.
The apex of the “classic” Scheuermann kyphosis is located at the midthoracic spine, the lower thoracic spine, or the thoracolumbar junction. Edgren and Vainio first described similar vertebral changes that may occur also in the lumbar spine (atypical Scheuermann, lumbar Scheuermann).
Incidence
The incidence of Scheuermann disease varies. Sorensen reported a 0.4% to 8% incidence in the population. Bradford noted an incidence as great as 10%. In a review of 1384 cadaveric specimens, Scoles and colleagues reported a prevalence of 7.4%. Scheuermann disease affects the growing, maturing spine and is usually identified in adolescents between 11 and 17 years of age.
In the past, Scheuermann disease was thought to be more common in men than in women. The male-to-female ratio is actually considered to be close to 1. Additionally, there is an increased incidence of spondylolysis in patients with thoracic Scheuermann kyphosis.
A familial occurrence of the disease has been described. Damborg and associates reviewed 35,000 twins. They found a prevalence of Scheuermann disease of 2.8% (3.6% among males and 2.1% among females). The concordance for monozygotic twins was significantly greater than that for dizygotic twins, and the hereditability was 74%. These findings suggest a strong genetic contribution to the etiology of the condition.
Pathogenesis
The etiology of Scheuermann disease remains unknown. However, several theories have been suggested. The increased release of growth hormone, defective formation of collagen fibrils with subsequent weakening of the vertebral end plates, juvenile osteoporosis, trauma, vitamin A deficiency, poliomyelitis, and epiphysitis are some of the theories.
Scheuermann disease may result from excessive stress on a weakened end plate during growth of the spine. Histologic studies demonstrate disorganized endochondral ossification, reduced collagen level, and increased mucopolysaccharide levels in the end plate with the disease. The main hypothesis is that disorganized endochondral ossification results from the defective growth of the cartilage end plate.
The weakness of the vertebral end plate likely results from a predisposing genetic background that influences the quality of matrix components (collagen types II and IX) and chondrocytes. An autosomal dominant form of inheritance is suspected. The main candidate genes are COL2A1 and COL9A3. An Arg cyst mutation in COL2A1 was found associated with a spondyloepiphyseal dysplasia similar to Scheuermann disease with severe osteoarthritis. The role of COL1A1 and COL1A2, initially suspected, was not confirmed.
Mechanical stress influences the severity of spinal impairment. This is consistent with several observations. First, some authors reported similar lesions of localized lumbar osteochondrosis in twin sisters, worse in the twin who practiced strenuous sports activities. Second, the prevalence of Scheuermann disease seems to be higher in manual workers who began work at a young age and in high-level athletes of sports involving large motions of the trunk in flexion/extension. Finally, repetitive strain on vertebral end plates in young rats led to typical Scheuermann lesions. A high body mass index may be another risk factor for Scheuermann disease.
Fotiadis and colleagues, investigating the length of the sternum of 10,057 students, found that 175 adolescents with Scheuermann disease had a short sternum. This short sternum might result from excessive pressure on the front part of vertebral bodies associated with a particular genetic background.
Clinical Features
The onset of Scheuermann disease usually appears around puberty, commonly as kyphosis of the thoracic (type I Scheuermann) or thoracolumbar spine (type II Scheuermann). These two entities differ both in location and by their clinical presentation. The deformity is often attributed to poor posture. This results in a delay in both diagnosis and treatment. Pain is often present; standing, sitting, and heavy physical activity may aggravate the pain (i.e., mechanical pain), which may or may not subside with cessation of growth. Adults who have untreated Scheuermann disease may have severe back pain, especially when the deformity is advanced.
Patients generally present with an angular thoracic or thoracolumbar kyphosis accompanied by a compensatory hyperlordosis of the lumbar spine. Sorensen described pain as the major symptom in 50% of patients with advanced disease. Advanced thoracic kyphosis can lead to thoracic spinal cord compression and paraparesis.
In addition to the kyphosis of the thoracic spine, affected individuals demonstrate varying degrees of structural scoliosis. Blumenthal and associates noted 85% of lumbar scoliosis among 50 patients with type I Scheuermann disease. Spondylolysis and spondylolisthesis are also common in the lumbar spine. Ogilvie and Sherman observed a 50% incidence of asymptomatic spondylolysis among 18 patients with type I disease. They postulated that the excessive hyperlordosis places stress on the pars of the L4 and L5 vertebrae, resulting in the spondylolysis. Clinical examination often reveals tight hamstrings as well as a popliteal angle of less than 30 degrees and subtle neurologic findings. Tight hamstrings have been implicated as a possible cause of sagittal decompensation.
Increased cervical lordosis also develops as a compensatory mechanism and causes the head to protrude forward (gooseneck deformity), producing a negative sagittal balance with the C7 plumb line lying posterior to the sacral promontory .
Radiographic Features
Routine radiographic studies obtained for evaluation of the patient with Scheuermann kyphosis should include anteroposterior and lateral radiographs of the entire spine via full-length 3-foot long films (scoliosis views). The lateral radiograph should be obtained with the patient standing, with knees and hips fully extended and arms out and away from the spine. The patient should be looking forward.
In addition, a hyperextension lateral image of the thoracic spine, preferably over a bolster, should be obtained to assess flexibility of the spine. The lateral radiograph may verify some or all of the following typical changes of Scheuermann kyphosis:
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Schmorl nodes
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Kyphosis of the involved spinal segment
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Ventral vertebral body wedging
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End plate irregularity
Both the vertebral wedging and kyphosis should be measured by the Cobb method. When evaluating serial radiographs to document progression, care should be taken to ensure that the same end vertebral bodies are measured each time. The normal range of thoracic kyphosis is 20 to 45 degrees on a standing lateral radiograph as measured by the Cobb method.
The kyphosis in Scheuermann disease is usually incompletely reducible with postural and positional changes. The vertebra with the greatest ventral deformity is located at the apex of the kyphotic curve. The kyphosis may approach 100 degrees in advanced cases with a compensatory hyperlordosis of both the cervical and lumbar spine.
Vertebral wedging occurs during the primary ossification and increases during the secondary one according to Delpech’s law. The phenomenon could be described as excessive pressure on the vertebral end plate inducing vertebral wedging, and the wedging itself increases the mechanical stress on the vertebral end plate. This defective growth of the front part of the vertebral body maybe associated with excessive lengthwise growth (the Knutsson sign). Sometimes a flattening of the whole vertebral body can be observed with a lengthening of the adjacent vertebra as compensation (the Edgren sign).
A magnetic resonance image (MRI) taken before surgery is recommended to rule out any incidental thoracic disc herniation, epidural cyst, or possible spinal stenosis. The literature has shown such exceptional cases in various reports of neurologic complications in Scheuermann kyphosi. The MRI will also assess the lumbar spine discs, as disc degeneration of the lumbar spine may explain, in some cases, the pain rather than the kyphotic deformity itself.
Another factor associated with back pain is the size of the disc herniation (7.9 mm mean diameter in symptomatic patients versus 5.2 mm in asymptomatic patients).
It is important to differentiate Scheuermann kyphosis from a postural round-back deformity. Adolescents with postural round-back deformity have a slight to moderate increase in the degree of thoracic kyphosis (usually up to 60 degrees), which is less acutely angulated and may be associated with an accentuated lumbar lordosis. This type of kyphosis is flexible and not associated with muscle contractures. There is also a normal appearance of the vertebrae without evidence of wedging, end plate irregularity, or premature disc degeneration on imaging.
Natural History
The literature lacks agreement when it comes to the natural history of Scheuermann disease. The condition tends to be symptomatic during the teenage years. However, in the late teenage years, it often produces less pain. If the residual kyphosis in these patients remains less than 50 to 60 degrees, there is usually little discomfort in adult life.
In a long-term follow-up study, Sorensen noted pain in the thoracic region in 50% of patients during adolescence, with the number of symptomatic patients decreasing to 25% by the time of skeletal maturity. Later, other authors offered a contrasting view, stating that adults with Scheuermann kyphosis have a higher incidence of disabling back pain than do the normal population.
Two studies found an increased prevalence of back pain in the classical thoracic form. The first study involved a Finnish retrospective cohort with a 37-year follow-up of 49 patients (mean age 59 years); the prevalence of low back pain was 39%, which was 2.5 times higher than in the control population. The second study was a 32-year follow-up of 67 patients from North America that found an increased prevalence of thoracic back pain (28% versus 0% in the control population). In both studies, the presence of back pain was not associated with the degree or apex level of kyphosis. Restrictive lung disease was observed only when the kyphosis was > 100.
Murray and colleagues performed a study in 67 patients with Scheuermann kyphosis diagnosed by Sorensen’s criteria (i.e., physical examination, trunk strength, radiography, a detailed questionnaire, and pulmonary function testing). The patients had an a verage kyphotic deformity of 71 degrees, and average follow-up was 32 years. An age-matched comparison group was used as a control. Normal or above normal averages for pulmonary function were found in patients in whom the kyphosis was less than 100 degrees. Patients in whom the kyphosis was greater than 100 degrees and the apex of the curve was in the first to eighth thoracic segments had restrictive lung disease. The authors concluded that patients may have functional limitations but these did not result in severe limitations due to pain or cause major interference with their lives. Lowe and Kasten stated that adults with greater than 75 degrees of kyphosis can have severe thoracic pain secondary to spondylosis that can limit their activity.
In summary, patients experience wide variations in the natural history of Scheuermann kyphosis. Thoracic Scheuermann kyphosis greater than 100 degrees can be associated with reduced pulmonary function. There appears to be a subset of patients with refractory symptoms that justify the risk associated with intensive treatments such as bracing and surgical management.
Treatment
Treatment of Scheuermann disease includes spine- and trunk-specific exercises, postural exercises, bracing, and, for a very few patients, surgery. However, mild forms of the disease can be managed with advice and observation. Sports involving excessive pressure on the spine, such as weightlifting, and those with repetitive strains on the vertebra, such as rugby, must be avoided for all cases.
Indications for management of adult Scheuermann kyphosis include progression of the deformity, pain, cosmesis, and, rarely, cardiopulmonary or neurologic compromise.
The recommended treatment should be tailored to the individual on the basis of deformity progression, the severity of the curve, and symptomatology measured against the risk of surgery.
Nonoperative Treatment
Nonoperative treatment is classically indicated during the growth period if thoracic kyphosis exceeds 40 to 45 degrees and if radiologic signs of the disease are present. It includes postural, trunk, and spine conditioning exercises; bracing; and, rarely, casting.
Anti-inflammatory Medications
Nonsteroidal anti-inflammatory drugs (NSAIDs) may be useful short-term adjuncts to nonoperative care of the adolescent. They may also be considered for longer-term care in the adult with spondylosis and back pain.
Exercise
A trunk and spine conditioning program is recommended to relieve pain and to improve sagittal balance when the kyphosis can be reduced. Different exercise protocols include postural control, strengthening and stretching of the trunk, and musculotendinous stretching particularly of hamstring and pectoral muscles, which are often shortened and tight. Respiratory rehabilitation can be useful in case of restrictive lung disease.
Weiss and coworkers reported pain reduction of between 16% and 32% in a group of 351 patients with a painful Scheuermann kyphosis who were treated nonoperatively with physical therapy, osteopathy, manual therapy, exercises, and psychologic therapy. The remaining studies are simple case reports of minimal value in determining treatment methods.
Brace Treatment
Bracing and casting are of value only in patients with mobile kyphotic deformity and with a sufficient amount of growth remaining. The few available brace treatment studies are retrospective, have different inclusion criteria, and do not have control groups. The initial report of Bradford and colleagues regarding Milwaukee brace treatment of Scheuermann kyphosis in 75 patients demonstrated a 40% decrease in mean thoracic kyphosis and a 35% decrease in mean lumbar lordosis after an average of 34 months of brace wear.
By analogy with scoliosis, the brace should be worn 21 hours per day until the patient reaches skeletal maturity. Compliance may be worse with the Milwaukee brace than other braces, by virtue of the aesthetic and psychologic impact of the neck ring.
Gutowski and Renshaw reported on the use of Boston lumbar and modified Milwaukee orthoses for Scheuermann kyphosis and abnormal juvenile round back, with an average 26-month follow-up. Of the 75 patients in their group, 31% rejected the brace within 4 months.
Compliant patients had an improvement of 27% in the Boston group and 35% in the Milwaukee group. Whether the corrections were maintained over time is not known. Bracing can be expected to provide up to a 50% correction of the deformity, with some gradual loss of correction over time. Sachs and associates followed 120 patients for more than 5 years after discontinuation of the brace and demonstrated that 69% still had improvement of 30 degrees or more. The Milwaukee brace is the most commonly used brace. It is indicated when the apex of the kyphosis is at or above T8 and for the overweight patient or the female patient with large breasts. The underarm orthosis or thoracolumbosacral orthosis (TLSO) is indicated when the apex of the kyphosis is at or below T9.
The classic prerequisites for brace treatment of Scheuermann kyphosis include a progressive curve beyond 45 degrees. Patients with a kyphosis of up to 65 degrees may be successfully treated. Treatment using a Milwaukee brace was shown to be effective to relieve pain and correct curves less than 74 degrees in skeletally immature patients, but curves greater than 74 degrees have been associated with higher failure rates. Patients must have some flexibility and some remaining growth. Bracing or casting is known to be ineffective once the patient’s Risser sign is 4 or 5.
Surgical Treatment
Surgical intervention focuses on correction of kyphosis and prevention of deformity progression, but the primary goal is relief of associated pain. In general, potential surgical candidates have curves > 60 degrees and pain that is not relieved with nonsurgical measures. Surgery can also be considered in persons with curves that produce unacceptable cosmesis. Rarely, neurologic deficits have been reported to be an indication for surgery. These deficits can be related to disc herniation, tumors, epidural cysts, or the deformity itself. Cardiopulmonary indications for surgical intervention are rare and appear only in patients with curves > 100. A preoperative MRI of the thoracic spine should be obtained before surgery to rule out disc herniation or other canal pathology that may result in cord compression following deformity correction. The ultimate decision for surgical correction should be individualized. It may relate to the patient’s symptoms, self-perception, and sense of self-esteem. The surgeon’s training and level of skill in performing a safe, predictable correction also affect the decision-making process.
Biomechanical principles of the correction of the kyphosis include lengthening of the concavity (anterior column) and shortening of the convexity (posterior column). The goal of surgical intervention is a solid arthrodesis throughout the length of the kyphosis.
Intraoperative neuromonitoring of motor- and somatosensory-evoked potentials are recommended, and a wake-up test is performed if there is a > 50% drop in amplitude or a 10% increase in latency. Surgical management of Scheuermann kyphosis can be performed via posterior-only, anterior-only, or combined anterior-posterior approaches. Kostuik described a ventral-only approach with interbody fusion and ventral instrumentation with a Harrington distraction system augmented by postoperative bracing. He reported the results in 36 patients with a mean preoperative reduction from 75.5 to 60 degrees. Subsequently, ventral fusion has not gained significant acceptance for the correction of Scheuermann kyphosis.
Posterior-only approaches have the advantages of decreased blood loss and shorter surgical times, thereby avoiding the need for thoracotomy. These approaches do not interfere with the anterior blood supply to the spinal cord. However, posterior-only approaches may be unsuitable for patients with rigid curves that do not correct to < 50 degrees on hyperextension radiographs. Good results with posterior-only approaches have been reported so long as no anterior bony bridging has occurred at the time of surgery.
Because the anterior longitudinal ligament (ALL) is still intact, instrumentation introduced through the posterior-only approach is under continual tensile stress. As a result, an improper fusion technique increases the risk of implant failure and pseudarthrosis.
Early studies by Bradford and colleagues showed a higher incidence of loss of correction and inferior results with posterior-only approaches compared with combined anterior-posterior approaches. However, Harrington rods, hooks, and wires were primarily used in these studies.
Ponte and Slocardi presented an abstract detailing the results of posterior-only segmental correction using hooks and apical wide facetectomies. They reported excellent correction (48 degrees) and preservation of correction (a 3-degree loss) at 39 months of follow-up. Complications in this series included two patients with fractured lamina and two cases of postoperative paraplegia, which resolved with rod removal followed by brace immobilization.
The role of an additional anterior release is more important in large and rigid curves (75 degrees or greater that do not correct to less than 50 degrees on hyperextension lateral radiographs), which are spanning few levels and are creating an acutely angular deformity, especially in the presence of a bony ankylosis across the anterior aspect of the vertebral bodies and the anterior longitudinal ligament at the apex of the kyphosis.
However, with the use of all pedicle screw constructs and multiple-level osteotomies, the value of anterior release is to be reconsidered. Several major complications were mentioned in the literature including pneumothorax, lung collapse, chest infection, and hemothorax. More important, pulmonary function may not return to baseline, even at 2 years postoperatively. A series by Herrera-Soto and colleagues used video-assisted thoracoscopic anterior release and fusion combined with hybrid instrumentation posteriorly in 19 patients. Despite the less invasive nature of thoracoscopy, there were four significant pulmonary complications, including effusion, pneumothorax, and embolus.
The value of anterior release was also challenged when Johnston and colleagues advocated that shortening the posterior column with resection of lamina and facets in the apex corrects the deformity without disturbing the anterior column. With intact discs, no anterior column support is necessary to avoid collapse of the disc space should anterior fusion be delayed. If discectomy is not performed, there is no need to prevent the shortening of a released, elongated anterior column.
Wael and Koptan published a study aiming at comparing the results of segmental all pedicle screw constructs versus two-staged hybrid instrumentation in patients with Scheuermann kyphosis. They analyzed the amount of correction and incidence of complications. The study included 33 patients divided into two groups. The average age was 15 years and 16 years, respectively. The average preoperative dorsal kyphosis was 85.5 degrees (group 1) and 79.8 degrees (group 2).
The results of this study showed that the use of the multiple-level all pedicle screws technique allowed a rigid anchor for posterior correction of the deformity with less operative time, blood loss, and hospital stay without the need for anterior release, so a better correction was achieved and preserved with the use of all pedicle screw constructs. They also compared the results using single-staged multiple-level segmental osteotomies to results using apical Smith-Petersen osteotomies reported in other studies, and they achieved a similar degree of correction of the kyphosis that was maintained at follow-up with an equally acceptable loss of correction. Nevertheless, their total operative time and total blood loss were considerably less, possibly because of the simpler technique of this segmental osteotomy.
The selection of fusion levels for thoracic hyperkyphosis is the most important consideration in planning surgery. Improper fusion levels impair global sagittal balance and have a high risk of developing junctional kyphosis above or below the instrumentation.
However, the selection of fusion levels has been controversial. It is important to extend the fusion over the entire length of the kyphotic deformity. Most surgeons agree that the upper limit of the fusion must be the proximal end vertebra in the measured kyphosis. On the other hand, the exact criteria for the distal end of the fusion has not been established. The lower end vertebra is not thought to be appropriate to prevent junctional kyphosis. The end vertebra for the distal fusion level was not thought to be appropriate to prevent junctional kyphosis. The clinical significance of distal junctional kyphosis (DJK) is variable, but it appears suboptimal to have DJK at the end of a surgical kyphosis construct. Occasionally this will require revision surgery and is sometimes associated with pain over the distal level of the construct or prominent instrumentation.
Ascani and Rosa advocated extending the instrumentation and fusion one additional level into the area of the inferior neutral vertebra always including L1 in the arthrodesis. Wenger and Frick stated that posterior instrumented fusion from the T3-L2 level is necessary. The current consensus for the distal fusion level is to include not only the end vertebra but also the first lordotic disc beyond the transitional zone distally. However, even when these rules are implemented junctional kyphosis has been noted.
In 2009 Kyu-Jung Cho published a retrospective study that included 31 patients proposing that the distal end of the instrumentation should include the sagittal stable vertebra (SSV), which is defined as the most proximal vertebra touched by the posterior sacral vertical line (PSVL). The PSVL is a line drawn vertically from the posterior-superior corner of the sacrum on the lateral upright radiograph. The purpose of this study was to demonstrate the validity of this method for determining the appropriate distal fusion level in posterior instrumentation and fusion for thoracic hyperkyphosis by investigating the relationship among the SSV, the first lordotic vertebra (the vertebra just caudal to the first lordotic disc below the kyphotic deformity), and the lowest instrumented vertebra (LIV), and the relationship to postoperative radiographic evidence of junctional kyphosis.
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